Before we get close to boots on the ground, we need to carefully consider what military action is intended to achieve. Photograph: Andrew Parsons/PA

Discussion of military action against the Islamic State (Isis) is veering close to the stupidly binary – where someone either agrees with every as-yet-unspecified thing the government wants to do, or is accused of being blind to the danger and the atrocities.

If there is one thing we should have learned from the last decade it is surely the folly of committing to military action without a clear understanding of the precise objectives of the involvement, what we want to achieve or how long we are prepared to stay.

There is a humanitarian crisis in northern Iraq, Isis is engaging in mass murder and US president Barack Obama has quite rightly described the aim of previous US air strikes as being to “prevent an act of genocide”. Most people would consider it a situation that warrants action by the US and its allies.

But would the aim of that action be purely humanitarian, would it be to hold Isis back while the new Iraqi government finds its feet or would it be to somehow “defeat” Isis? Australia seems to be marching toward an involvement in further military action before we have had a chance to discuss this.

The Australian newspaper tells us “The Abbott government stands ready to help the US broaden its campaign against Islamic State terror fighters in Iraq with RAAF support for humanitarian and ultimately, combat roles if necessary.”

The New York Times tells us that “the United States has begun to mobilise a broad coalition of allies behind potential American military action in Syria and is moving toward expanded airstrikes in northern Iraq” and that Australia is one of the countries willing to join an air campaign.

The defence minister, David Johnston, signalled in an ABC interview that Australia could be willing to contribute Super Hornets to US-led air strikes and that the defence force is “at a high state of readiness”.

And the chief of the defence force, Air Chief Marshal Mark Binskin told the Age that Isis would sooner or later have to be defeated ‘’on the battlefield’’.

The national security committee of cabinet has been meeting regularly and Iraqi diplomatic representatives have been in parliament house.

But because no formal request has yet been made by the US, the government has not yet briefed the opposition about its intentions or deliberations, nor taken the parliament or the public into its confidence.

The prime minister has promised (in answer to a question from the Greens’ Adam Bandt), that “this government won’t commit forces without the fullest possible consideration, without the consideration of cabinet and without consultation with the opposition.”

The clearest answer to date came from foreign minister Julie Bishop, who said Australia “stood ready to consider any further requests from the US” with that consideration “based on an assessment of risk, what achievable humanitarian purpose might be achievable and what clear and proportionate role” there would be for Australia.

That’s still not entirely clear.

The government is also “consulting” on new anti-terror laws to deal with the domestic threat that could be posed by radicalised jihadist fighters trying to return from battles overseas. This is a real concern of the intelligence agencies, but we don’t yet know any details about the new laws, and as Asio chief David Irvine told the National Press Club on Thursday, they are still at an “in principle” stage.

At the same time the prime minister informed us there were new customs and border protection units operating at Sydney and Melbourne airports, expanding to other airports soon.

Given that customs embarrassingly let terrorist Khaled Sharrouf out of the country because he was travelling on his brother’s passport, it seems a good thing they now have extra resources, although as the opposition’s foreign affairs spokesman, Tanya Plibersek, pointed out Thursday, it may not have been so wise to announce the airports where they weren’t operating yet.

But it is also true that diverting discussion from the totally stalled budget to terrorism is politically good for the government. Liberal and Labor MPs are more than happy to concede this behind the scenes.

Determined not to be portrayed as “soft” on terrorism or national security, Labor is for the most part unwilling to say it loud.

When Labor senator Sue Lines claimed the prime minister was using national security as “a shield to try and deflect from the awful mess they’re in with their budget”, the immigration minister, Scott Morrison, was quick to pounce.

“I think that’s pathetic and if she doesn’t believe that the IS involvement in Iraq and Syria presents a genuine and real threat to Australia, then she is a muppet,” he said.

I’m not sure what Lines thinks, but it is entirely possible to think Isis presents a genuine and real threat to Australia and the world, and also to think that it helps the government to discuss national security rather than the budget.

It is possible to think the Isis threat may well justify action by US and its allies, and at the same time want to discuss and consider the objectives and consequences of the exact type of action that is proposed.

It is possible to understand that returning jihadist fighters pose a potential threat to Australia and still want to scrutinise the detail of the laws the government says are needed to address it.

And presenting any of those discussions as a binary “with us or against us” proposition – even when all the details remain under wraps – risks fracturing the community support that is actually crucial for the success of any military action or proposed security measures.